60 FRAGMENTS OF SCIENCE. 



through the operation of the same force that pulls an 

 apple from its tree. This all-pervading force, which 

 forms the solder of the material universe, and the con- 

 ception of which was necessary to Newton's intellectual 

 peace, is called the force of gravitation. 



Gravitation is a purely attractive force, but in elec- 



/tricity and magnetism, repulsion had been always seen 

 to accompany attraction. Electricity and magnetism 

 are double or polar forces. In the case of magnetism, 

 experience soon pushed the mind beyond the bounds of 

 experience, compelling it to conclude that the polarity 

 of the magnet was resident in its molecules. I hold a 

 magnetised strip of steel by its centre, and find that 

 one half of the strip attracts, and the other half repels, 

 the north end. of a magnetic needle. I break the strip 

 in the middle, find that this half, which a moment 

 ago attracted throughout its entire length the north 

 pole of a magnetic needle, is now divided into two new 

 halves, one of which wholly attracts, and the other of 

 which wholly repels, the north pole of the needle. 

 The half proves to be as perfect a magnet as the whole. 

 You may break this half and go on till further breaking 

 becomes impossible through the very smallness of the 

 fragments ; the smallest fragment is found endowed with 

 two poles, and is, therefore, a perfect magnet. But 

 you cannot stop here : you imagine where you cannot 

 experiment ; and reach the conclusion entertained by 

 all scientific men, that the magnet which you see and 

 feel is an assemblage of molecular magnets which you 

 cannot see and feel, but which, as before stated, must 

 be intellectually discerned. 



Magnetism then is a polar force ; and experience 

 hints that a force of this kind may exert a certain struc- 

 tural power. It is known, for example, that iron filings 

 titrewn round a magnet arrange themselves in definite 



